UF Study: U.S. Population Has Moved Away from Rivers, Toward Groundwater

GAINESVILLE, Fla. — Look at a map of any major city, and chances are you’ll find a river nearby. That’s no accident: people have historically lived close to waterways, using them for drinking water, agriculture and transportation.

But according to a recent study by a University of Florida researcher, since 1870, that trend has reversed in the United States. During this period, people moved farther away from rivers and toward another source of water not visible on a map: groundwater.

Reliance on groundwater has implications for how population centers will evolve, said James Jawitz, the study’s lead author.

“You need considerable infrastructure and technology to move water from the ground to where people live. As populations continue to move away from rivers, you’ll need adequate investment in water transport systems to sustain stable water supplies,” said Jawitz, professor of soil and water sciences in the UF Institute of Food and Agricultural Sciences.

Groundwater is important in almost every state in the U.S., he said.

Compared to other states, Florida is one of the most reliant on groundwater, drawing about 90 percent of its supply from the aquifer, Jawitz said. In California and Texas, groundwater accounts for about half the water supply. Then there are very arid states, such as New Mexico, which also gets 90 percent of its water from the ground.

Jawitz co-authored the study with Yu Fang, who was a doctoral student in the UF/IFAS College of Agricultural and Life Sciences at the start of the study and is now a post-doctoral researcher at Tsinghua University. Fang graduated from the UF/IFAS CALS School of Natural Resources and the Environment in 2016.

Jawitz and Fang initially hypothesized population movement away from rivers. They tested this idea by overlaying historical human population data with maps of major rivers and groundwater accessibility. Previous studies have examined the distance of contemporary human settlements from rivers, but this is the first to look at that distance over a long timescale while also considering groundwater.

Starting at 1790, they observed how the relationship between population and water sources changed over time. Their analysis showed an even stronger relationship than predicted. “These types of relationships were hypothesized but the strength and clarity of the signals was surprising,” Jawitz said.

Two factors contributed to people moving away from rivers, he said.

“First, during pre-industrial periods people moved closer and closer to rivers, indicating the growing importance of urbanization of major cities along rivers. Then this trend dramatically reversed in 1870, at the peak of the industrial revolution and just as the transcontinental railroads were completed,” Jawitz said. “Overland transport options allowed people, for the first time, to live in great numbers in places that were not adjacent to major waterways. Second, in the twentieth century population growth rates in areas underlain by groundwater were much higher in areas with high-recharge, productive aquifers.”

As cities have continued to grow, increasing demand for water has exceeded local supplies. This is true in cities such as Los Angeles, Phoenix and Atlanta, where water is now imported from sources hundreds of miles away.

The study is published in the journal Nature Communications.

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